Migraine affects one in four women, and one in ten men, over a lifetime. It also causes considerable suffering. Like many diseases that mainly affect women, it is poorly understood. But the very fact that migraine is more frequent in women can yield clues to its origins. Migraine is more severe during the reproductive years, but improves after menopause. It worsens around menstruation, but improves during pregnancy. This suggests a hormonal role in its origins. We propose to study the role of the female sex hormones estrogen and progesterone in cortical spreading depression (CSD), the event thought to underlie certain forms of migraine. The goal is to understand the process specifically in women, as they suffer most from this disease. Using a technique called optical intrinsic signal imaging (OIS), we can directly image CSD in mice. We can use this mouse model to study the role of estrogen and progesterone in CSD. Our preliminary data suggests an inhibitory effect of progesterone on CSD, and estrogen is known to be excitatory to neuronal preparations, thus there is a rational basis for this study. We propose that the different levels of these hormones over the menstrual cycle, pregnancy, and menopause cause changes in the susceptibility to CSD. We will test this by measuring threshold for and response to CSD at these different stages in female mice. Next, we will evaluate the effect of these hormones on CSD in male and ovariectomized female mice, in order to isolate their roles without the effect of endogenous hormones. We will also examine the effects of estrogen and progesterone on the surface vessels of the brain during CSD. These vessels are thought to respond to CSD in such a way that they generate the pain felt by the migraine sufferer. A hormonal role is possible in these changes, as estrogen is a potent vasodilator. Finally, we will evaluate the effects of estrogen and progesterone on astrocyte calcium waves, which propagate in a manner remarkably similar to CSD. As astrocytes respond to both estrogen and progesterone, it is possible that they participate in the hormonal modulation of migraine. We will test the effects of estrogen and progesterone in brain slices and in culture. It is hoped that these experiments will shed light on the basic mechanisms of migraine, in particular the question of why migraine affects women so much more than men.